Many modern communication systems employ a signaling pattern that has useful information in both the time and frequency domains. One useful tool that has traditionally been available on some spectrum analyzers is the spectrogram, which can be used to view both the time and frequency domains simultaneously. The spectrogram has one axis for the time domain, one axis for the frequency domain, and uses color to represent power levels.
One system that uses a hopping pattern is the WiMedia Alliance (formerly known as the Multiband OFDM Alliance (MBOA)) format, one example of which is a wireless USB signal. The hopping pattern used by a WiMedia signal is called a time-frequency code .(TFC), and there are two types of patterns. The first type is called Time-Frequency Interleaved (TFI), and includes signals that hop in various patterns among the three frequency bands in the band group. The second type is called Frequency-Fixed Interleaved (FFI), in which the signal does not hop but stays in one frequency band. The length of the TFC code is 6 symbols, so it is repeated at least several times during a packet. Each frequency band is 528 MHz wide and there are 3 frequency bands in the first band group defined by WiMedia. Therefore, the total signal is almost 1.6 GHz wide.
Traditionally, a spectrum analyzer is used for generating spectrograms. However, for analyzing ultrawideband signals, an oscilloscope must be used to capture the signal because the real-time bandwidth of a spectrum analyzer is too limited. If the oscilloscope has a way of computing and displaying a spectrogram, this algorithm can take that output and determine the time-frequency code. If a spectrogram is not available on the oscilloscope, the captured data will have to be post-processed with a tool that can provide a spectrogram (MATLAB is one example).
While a spectrogram is a very useful tool for examining signals with time and frequency information, it is a general-purpose tool and does not provide for automatic detection of signal parameters such as the time-frequency code.
A consumer radio can determine the TFC code on a received signal by demodulating the signal and decoding the preamble and header of a WiMedia signal. A test and measurement device could also determine the TFC code in this manner, but this method would involve a custom software program to demodulate the signal and decode the information in the header.
The solution must also be able to work on an off-the-air signal, since consumer devices such as a wireless USB radio will not have the ability to directly connect to a test and measurement device. However, prototype radios will have a direct connect option, so the solution needs to work correctly in both cases.